The present invention relates to the general field of turbine engine walls that are cooled by multiple perforations. The invention relates more particularly to an annular shroud for a forward flow or a reverse flow combustion chamber, to a cooled annular nozzle wall cover, or to an annular jacket for protecting a reheat chamber.
Typically, in those various portions of a turbine engine, the wall in contact with hot gas is subjected to the high temperatures of the gas and is provided with multiple perforation orifices, that are generally inclined at an angle of 60° relative to the normal to the wall so as to enable air flowing outside the wall to penetrate to the inside of the wall and form films of cooling air along its hot side.
Unfortunately, in order to take account of the way thermal stresses increase as an engine ages, the number and the distribution of cooling orifices needs to be designed to provide the maximum level of porosity as required at the end of the lifetime of the engine.
As a result, firstly a new engine at the beginning of its lifetime has a level of porosity that is not optimized, so the maximum air flow rate then used for cooling the walls reduces the overall performance of the turbine engine, and secondly this additional cooling increases pollution by causing combustion products to congeal. Furthermore, when the multiple perforations used are of the gyratory type, thermal efficiency is close to 1 even though the materials used for the walls are capable of withstanding considerably higher temperatures without prejudicing the lifetime of the turbine engine.